Commissioning Residential Ventilation Systems: A Combined Assessment of Energy and Air Quality Potential Values
Due to changes in building codes, whole-house mechanical ventilation systems are being installed in new California homes. Few measurements are available, but the limited data suggest that these systems don't always perform as code and forecasts predict. Such deficiencies occur because systems are usually field assembled without design specifications, and there is no consistent process to identify and correct problems. The value of such activities in terms of reducing energy use and improving indoor air quality (IAQ) is poorly understood. Commissioning such systems when they are installed or during subsequent building retrofits is a step towards eliminating deficiencies and optimizing the tradeoff between energy use and IAQ.
The goal of this study was to determine the potential value of commissioning residential whole- house ventilation systems that are intended to comply with California's Title 24 residential ventilation requirements. A computer modeling approach was used to assess the impact on occupant health and building energy use of malfunctioning whole-house ventilation systems. Energy and IAQ impacts were quantified and then compared by using the Time Dependent Valuation (TDV) approach for energy and a Disability Adjusted Life Year (DALY) approach for IAQ. Results showed that health benefits dominated energy benefits independently of house size and climate. Providing minimum airflow rates to comply with ASHRAE Standard 62.2 alone was not a sufficient metric for commissioning whole-house ventilation systems, due to the strong dependence of IAQ on indoor contaminant emission rates. Instead, the metric should be net present value of the combined energy and IAQ benefits to the consumer and commissioning cost decisions should be made relative to that value even if that means ventilating to exceed the ASHRAE 62.2 minimum.
As a consequence of combining IAQ and energy costs, the beginnings of an approach to optimize the ventilation rates of homes was established.